The invention relates to an electrode for discharge lamps having a pin at least partially surrounded by a solid body.
Electrodes of the type mentioned in the introduction are used in discharge lamps in order to release or receive electrons during a gas discharge. The electrodes each contain a pin, at the free end of which electrons either emerge from the pin or enter it at this end, wherein the pin is generally partially surrounded by a cooling body in the proximity of its free end, which cooling body is usually formed from a wire wound around the pin. It has been shown that both the application of such a cooling body formed from a wound wire on the pin and also a robust attachment of the cooling body to the pin can only be achieved at a high technical cost, wherein the results with respect to a firm attachment of the cooling body to the pin are not satisfactory.
It is therefore the object of the invention to create an electrode for discharge lamps, wherein the cooling body is applied to the pin in a simple manner and is firmly connected to the pin thereby forming a robust unit.
For an electrode of the type mentioned in the introduction, this object is achieved in that the solid body is produced from a high-melting material.
Preferred embodiments of the invention are the subject of the subordinate claims.
In the electrode in accordance with the invention it is achieved, by the feature of the solid body being formed from a high-melting material, that the solid body also holding the function of a cooling body can be produced as a solid block which can be firmly connected to the pin both by reason of is material composition and also its dimensions.
In accordance with a preferred embodiment of the electrode in accordance with the invention, the solid body is formed from a material which has a melting point above 1800xc2x0 C.
The solid body is preferably formed from tungsten.
The solid body is preferably in the form of a cylinder in which an axial bore is introduced. The axial bore is dimensioned in such a way that the pin of the electrode can be introduced into the bore. After the pin has been introduced into the axial bore of the solid body, the solid body can be connected to the pin by a number of different methods to form a fixed unit as explained in more detail hereinunder. In accordance with a preferred embodiment of the electrode in accordance with the invention the bore is introduced into the cylinder by means of a laser, in particular a Nd:YAG laser.
In accordance with an important embodiment of the electrode in accordance with the invention, the solid body is composed of a plurality of partial solid bodies disposed one after the other. In this way it is achieved that particularly long electrode bodies in accordance with the invention can be produced which cannot be produced in a single-piece form by reason of the limited penetration depth of a laser beam.
In accordance with another important embodiment of the electrode in accordance with the invention the solid body-side end of the pin is welded to the end of the solid body surrounding it. This welding is preferably carried out by means of a laser, in particular a Nd:YAG or CO2 laser, and brings about the effect that the common end of the pin and of the solid body surrounding it is formed in the manner of a convex cap, of which the edge region forms a transition to the solid body. A cap formed in this way for the electrode in accordance with the invention comprises the advantage that it is particularly effective and resistant to wear.
In accordance with an important embodiment of the electrode in accordance with the invention, the solid body is provided with at least one transverse bore. If a transverse bore of this type is introduced into a solid body before an axial bore is introduced it permits removal to the outside of the vaporisation particles which arise when the axial bore is introduced by means of the laser. The formation of an axial bore by laser beams is thus particularly effective by reason of the rapid escape of the vapour particles thus effected from the region penetrated by laser beams. Furthermore, by means of the introduction of a transverse bore into a solid body, the possibility is created of welding the solid body to the pin at an additional fixing point than just the cap. Alternatively, the possibility is thereby created of welding the solid body to the pinxe2x80x94without welding the capxe2x80x94only at the locations where transverse bores are provided. The welding of these fixing points is preferably also carried out by laser beams. The introduction of transverse bores into the solid body also makes it possible to introduce or deposit emission pastes into the transverse bores. Emission pastes are generally materials which promote an electron emission of the electrode. In this embodiment of the electrode in accordance with the invention, the solid body therefore fulfills the function of increased electron emission in addition to the cooling function. The emission paste contains, for example thorium oxide.
The bore of the solid body of the electrode in accordance with the invention preferably comprises an inner diameter which is larger than the diameter of the pin, wherein the intermediate space between the solid body and the pin is filled with a melt. The melt preferably contains molybdenum. It is also possible, however, to consider tantalum, niobium, titanium or platinum. In this way a robust connection between the solid body and the pin is created in each case. As an alternative to a melt, the solid body can be shrunk mechanically by means of a plurality of stamps acting inwardly from the outside, to such an extent that it comes into a mechanically firm connection with the pin.
In the case of the electrode in accordance with the invention, the solid body is preferably welded to the pin at one or more fixing points, wherein the corresponding welding process is preferably achieved by laser radiation. A firm mechanical connection between the solid body and the pin is also made possible by a process for directly welding the solid body to the pin, carried out, in particular, at a plurality of fixing points, in the region of common outer contact edges or in the region of transverse bores.